Superheterodyne receiver



July 10, 1934. K. POSTHUMUS ET AL SUPERHETERODYNE RECEIVER Filed Jan. 5, 1932 WEYERS 5 U w SH .fl Z .m N U E SD mum A .ILH KT Y B Patented July 10, 1934 UNITED STATES SUPERHETERODYNE RECEIVER Klaas Pcsthumus an d Theodorus Josephus Weyers, Eindhoven, Netherlands, assignors to Radio Corporation of America, a corporation of Delaware Application January 5,

In Germany '7 Claims.

The present invention relates to radio receivers, and more particularly to improvements in, or relating to, superheterodyne receivers.

In superheterodyne receivers the oscillations produced by a local oscillator must be caused to heterodyne with the oscillations which come from the transmitting stations to be received, and which, if desired, may be amplified beforehand. For this purpose the local oscillator is coupled with a circuit in which these incoming oscillations are developed, and the combined oscillations are supplied to the grid of the detector tube. The amplitude of the oscillations arriving at the said grid depends as a rule on the frequency even within the wave range of the receiver. This must be ascribed substantially to the difference in the frequencies to which the two coupled circuits are tuned. This difference is invariable, and with high frequencies it is, therefore, proportionally smaller than with low frequencies. Moreover, the kind of oscillator and its manner of coupling also play a part.

It is, however, advisable to ensure that the amplitude of the oscillations on the grid of the above mentioned detector is as independent as possible of the frequency, at least within the wave-range of the receiver. According to the present invention, this result may be obtained by such a choice of the coupling of the local os- O cillator with the circuit of the oscillations received that this coupling is dependent on the frequency in the same measure, but in opposite sense, as otherwise would be the amplitude of the local oscillations applied to the detector grid. For example, if, as is mostly the case, the amplitude of the local oscillations on this grid should increase with the frequency, the harmful effect of this increase may be neutralized according to the invention, by a capacitive coupling of the local oscillator with the receiver.

The novel features which we believe to be characteristic of our invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically one circuit arrangement whereby our invention may be carried into effect.

Only those parts of a superheterodyne receiver are shown in the diagram which are necessary for the understanding of the invention. The incoming high frequency oscillations of the station to be received are brought to development 1932, Serial No. 584,785 June 30, 1931 in the anode circuit 2 of an amplifier tube 1, said circuit being tuned to the frequency p of these oscillations. A condenser 3 of the circuit 2 is included at the same time in a second circuit 4 connected to the grid circuit of an oscillator tube 5 and tuned to the frequency pic, in which a is the desired frequency of the so-calied mean or intermediate frequency or beat oscillation.

The oscillations of the oscillator which have the frequency pia are transmitted to the circuit 2 in which they occur the stronger the smaller percentage of the frequency p the frequency difference a is, or in other words the higher the frequency p is. The two circuits 2 and e are, however, capacitively coupled with one another by the condenser 3, and this coupling is the looser the more the frequency increases, and vice versa so that one has two mutually opposite actions. The anode circuit of the oscillator tube 5 has inserted in it a coil 6 inductively coupled with a coil 7 as at M in the grid circuit 4. Owing to this inductive retroactive coupling the tube 5 generates oscillations the amplitude of which increases with the frequency, and conversely. This circumstance, too, must therefore be taken into account 0 in the choice of the degree of coupling between the circuits 2 and 4.

If the frequency 10 varies, the various abovementioned influences exerted on the amplitude of the oscillations of the oscillator which penetrate into the circuit 2 and further on consequently neutralize each other. These oscillations are impressed, therefore, through the blocking condenser 8 to the grid of the detector tube 9 with an amplitude substantially independent of the frequency. If instead of the inductively backcoupled oscillator 5, use would be made of an oscillator whose oscillation amplitude is connected in another manner with the frequency, it would be necessary to choose a correspondingly modified coupling or a correspondingly modified degree of coupling between the circuits 2 and 4.

What is claimed is:

1. In a superheterodyne receiver, a radio frequency amplifier, a local oscillator, an oscillation circuit in the output of the amplifier tuned to signal frequency, an oscillation circuit in the input of the oscillator tuned to the oscillation frequency, an untuned reactance coupling both said oscillation circuits, a detector, and an untuned reactance connected to the high potential end of said circuit tuned to the signal frequency for impressing the combined signal and local oscillations upon the detector input. I

2. In a superheterodyne receiver, a local oscilla'tor including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit incuding a coil and a variable tuning condenser adapted to tune the circuit over a range of si nal frequencies differing from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, and an additional untuned reactance conductively connected to the coil of said signal circuit, for impressing the co1nbined signal and local oscillations in the signal circuit on the detector input.

3. In a superheterodyne receiver, a local oscillator including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit including a coil and a variable tuning condenser adapted to tune the circuit over a range of signal frequencies differing from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, and a condenser connected to the high potential end of the coil in the signal circuit, for impressing the combined signal and local oscillations in the signal circuit on the detector input, both said first two coupling means being so chosen that the amplitude of the oscillations transmitted to the detector input is independent of frequency.

4. In a superheterodyne receiver, a local oscillator including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, inductance means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit including a coil and a variable tuning condenser adapted to tune the circuit over a range of signal frequencies difiering from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, capacitative means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, having a control electrode and a condenser having one side connected to said electrode and a conductive connection between its other side and the coil of said signal circuit, for impressin the combined signal and local oscillations in the signal circuit on the detector input.

5. In a superheterodyne receiver, a local oscillator including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit including a coil and a variable tuning condenser adapted to tune the circuit over a range of signal frequencies differing from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, and an additional untuned coupling means, for impressing the combined signal and local oscillations in the signal circuit on the detector input and a radio frequency amplifier tube preceding said signal circuit, the latter being connected in the ouput of the amplifier.

6. In a superheterodyne receiver, a local oscillator including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, inductance means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit including a coil and a variable tuning condenser adapted to tune the circuit over a range of signal frequencies differing from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, capacitative means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, and means independent of both said coupling means, for impressing the combined signal and local oscillations in the signal circuit on the detector input, said last impressing means consisting of a condenser connected between the grid of the detector tube and the high alternating current potential side of the signal circuit.

'7. In a superheterodyne receiver, a local oscillator including a tube provided with a resonant grid circuit, said grid circuit including a coil and a variable tuning condenser adapted to tune the grid circuit over a range of oscillation frequencies, means for reactively coupling the plate and grid circuits of the tube so that the amplitude of oscillations varies directly with frequency, a signal circuit including a coil and a variable tuning condenser adapted to tune the circuit over a range of signal frequencies differing from said oscillation range by an intermediate frequency, means for simultaneously varying the condensers, means for reactively coupling the signal and oscillation circuits so that the coupling varies inversely with frequency, a detector tube, and an additional untuned coupling member conductively connected to the coil in said signal circuit, for impressing the combined signal and local oscillations in the signal circuit on the detector input and capacities in said oscillator grid circuit for maintaining said intermediate frequency constant throughout said ranges.

KLAAS POSTHUMUS. THEODORUS JOSEPHUS WEYERS. 

